436 COSMOS. 



character in regard to the composition and association of 

 their mineral aggregate. On the great transverse fissure 

 which, extending from sea to sea almost entirely in a direc- 

 tion from west to east, intersects a chain of mountains, or, 

 more properly speaking, an uninterrupted mountainous swell, 

 running from southeast to northwest, the volcanoes occur in 

 the following order: Colima (13,003 feet), Jorullo (4265 

 feet), Toluca (15,168 feet), Popocatepetl (17,726 feet), and 

 Orizaba (17,884 feet). Those situated nearest to each other 

 are dissimilar in the composition which characterizes them, 

 a similarity of trachyte occurring only alternately. Colima 

 and Popocatepetl consist of oligoclase, with augite, and con- 

 sequently have the trachyte of Chimborazo or Teneriffe; 

 Toluca and Orizaba consist of oligoclase with hornblende, 

 and consequently have the rock of yEgina and Kozelnik. 

 The recently-formed volcano of Jorullo, which is scarcely 

 more than a large eruptive hill, consists almost alone of 

 scoriaceous lavas, resembling basalt and pitch-stone, and 

 seems more like the trachyte of Toluca than that of Colima. 

 In these considerations on the individual diversity of the 

 niiueralogical constitution of neighboring volcanoes, we find 

 a condemnation of the mischievous attempt to introduce a 

 name for a species of trachyte, derived from a mountain 

 chain, chiefly volcanic, of more than 7200 geographical miles 

 in length. The name of Jura limestone, which I was the 

 first to introduce,* is unobjectionable, because it is taken 

 from a simple unmixed rock from a chain of mountains 

 whose antiquity is characterized by its containing organic 



* In the course of a geological tour which I made, in 1795, through 

 the south of France, western Switzerland, and the north of Italy, I 

 had satisfied myself that the Jura limestone, which Werner reckoned 

 among his muschel-kalk, constituted a peculiar formation. In my 

 treatise on subterranean gases, published by my brother, Wilhelm von 

 Ilnmboldt, in 1799, during my residence in South America, this 

 formation, which I provisionally designated as Jura limestone, was for 

 the first time mentioned (s. 39). This account of the new formation 

 was immediately transferred to the Oberbergrath Karsten's mineral- 

 ogical tables, at that time so generally read (1800, p. 64, and preface, 

 p. vii.). I named none of the petrifactions which characterize the 

 Jura formation, and in relation to which Leopold von Buch has ac- 

 quired so much credit (1839) ; I erred likewise in the age ascribed by 

 me to the Jura formation, supposing it to be older than muschel-kalk, 

 on account of its propinquity to the Alps, which were considered older 

 than Zechstein. In the earliest tables of Buckland, on the Superpo- 

 sition of Strata in the British Islands, the Jura limestone of Humboldt 

 is reckoned as belonging to the upper oolite. Compare my Essai 

 Geoyn. sur le Giscmcnt dcs Roches, 1^23, p. 281. 



